Electric vehicle with secondary battery power storage system

ABSTRACT

The present invention provides a distributed secondary battery type power storage system capable of maintaining the soundness of the secondary battery and of efficient electric power charging and discharging operations. The secondary battery power storage system comprises a secondary battery connected to a load, a charge/discharge unit connectable to a power system and connected to the secondary battery, and a plurality of loads connected to the charge/discharge unit. A power receiving object is selected and a capacity is determined on the basis of information about the operating condition of the plurality of loads, and the surplus electric power remaining in the secondary battery after feeding electric power from the secondary battery to the load is fed to the selected power receiving object through the charge/discharge unit. The secondary battery power storage system is capable of maintaining the soundness of the secondary battery and of efficient charging and discharging operation.

CONTINUATION STATEMENT

This is a continuation application of U.S. patent application Ser. No08/606,226, filed Feb. 23, 1996, still pending now U.S. Pat. No.5,834,922, which is a continuation of U.S. patent application Ser. No.08/363,372, filed Dec. 23, 1994, now abandoned.

BACKGROUND OF INVENTION

Field of Invention

The present invention relates to a secondary battery electric powerstorage system and, more particularly, to a battery system which isprovided with evaluation means of the soundness and the residual powerof a battery, the distribution of the surplus electric power of abattery, and the optimum charge/discharge control of a battery. Mostsecondary batteries for automobiles, uninterrupted power supplies andthe like have been lead-acid batteries.

The diffusion of electric power storage systems and electric vehicles,and the development of secondary batteries capable of storing electricpower in a high energy density have been strongly desired to meet risingnecessity for the leveling of power demand and progressively increasingdemand for global environmental protection, and the development of newbatteries has been expected.

Various kinds of large-capacity secondary batteries includingnickelcadmium batteries, nickel-metal hydride batteries, lithiumbatteries and sodium-sulfur batteries will come onto the market in thefuture for various purposes. When managing batteries, appropriatecharging and discharging of batteries according to their characteristicsare essential to securing the soundness and the long life of batteries.Each battery has specific charge/discharge, temperature, rate andself-discharge characteristics. These characteristics vary from batteryto battery.

In view of the convenience of using the battery, the residual capacityof the battery must be known as accurately as possible. Chargingsystems, temperature management and methods of determining the residualcapacity for each of those batteries have been proposed. There have beenknown, for example, methods of detecting the residual capacity on thebasis of only voltage (Japanese Patent Laidopen (Kokai) Nos. 58-85179and 61-135335), a method of managing the residual capacity on the basisof voltage and current (Japanese Patent Laid-open (Kokai) No. 52-32542),methods of managing the residual capacity on the basis of current andtime (Japanese Patent Laidopen Nos. 50-2130, 56-26271 and 59-28678), amethod of managing the residual capacity on the basis of measuredcapacitance (Japanese Patent Laid-open (Kokai) No. 2-301974), a methodof managing the residual capacity on the basis of voltage, current andtemperature (Japanese Patent Laid-open (Kokai) No. 2-170372), a methodof managing the residual capacity on the basis of internal resistance(Japanese Patent Laid-open (Kokai) No. 3-163375), a method of managingthe residual capacity that integrates current and takes chargeefficiency, discharge efficiency and temperature characteristics intoconsideration (Japanese Patent Laid-open (Kokai) No. 63-208773), andmethods of determining the residual capacity on the basis of thespecific gravity of the electrolytic solution (Japanese Patent Laid-open(Kokai) Nos. 56-24768, 57-88679 and 57-210578).

The capacity of a battery is dependent also on the charge and dischargehistory of the battery. For example, the capacity of nickel-cadmiumbatteries and nickel-metal hydride batteries decreases due to memoryeffect if shallow discharge and charge are repeated. In lithiumbatteries, lithium is accumulated on the positive electrode and materialforms on the negative electrode to degrade the battery. If thecharge/discharge balance is destroyed, the power of the lithium batterymust be discharged after due consideration of the charge capacity. It isvery important with combination batteries to know the charged capacity.Since the variation of the voltage of nickel-metal hydride batteries, ascompared with that of nickel-cadmium batteries, in the final stage ofcharging is obscure, nickel-metal hydride batteries may be overchargedcausing drying of the electrolyte or increase in the internal pressureand entailing safety problems unless nickel-hydrogen batteries arecharged after due consideration of the discharge capacity. Since thecapacity of batteries is greatly dependent on temperature, charging rateand discharging rate, the charge and discharge history of batteries mustbe taken into account. Charging systems have been studied with suchproblems in view. For example, a charging system disclosed in JapanesePatent Laid-open (Kokai) No.4-308429 charges a battery after detectingthe fully discharged condition of the battery from the end voltage ortime to solve problems due to memory effect, and a charging systemdisclosed in Japanese Patent Laid-open (Kokai) No. 61-81139 charges abattery after detecting the fully discharged condition of the batteryfrom the end voltage or time to prevent overcharge.

A method of determining the residual capacity of a battery on the basisof the specific gravity of the electrolyte is applicable only tolead-acid batteries. Although a method of managing the residual voltageon the basis of the voltage is effective when applied to lead-acidbatteries and lithium batteries the voltage of which variescomparatively widely during charging and discharging, the same isunsuitable for application to nickel-cadmium batteries and nickel-metalhydride batteries the residual capacity of which cannot be determined onthe basis of only the voltage. It is difficult to predict the residualcapacity accurately on the basis of current and temperature or on thebasis of time besides on the basis of voltage under operating conditionwhere discharge rate changes. When managing the residual capacity of abattery on the basis of measured internal resistance or capacitance, itis difficult to determine whether the increase of the internalresistance is due to the deterioration of the battery or whether theincrease of the internal resistance is due to the exhaustion of thebattery unless the mode of deterioration of the battery is preciselyknown. The management of the residual capacity on the basis ofintegrated current, charging efficiency, discharging efficiency andtemperature characteristics allows one to predict the residual capacityconsiderably accurately, however, it is difficult to determine theresidual capacity unless the capacity of the battery is known when thecapacity of the battery is reduced greatly or the self-discharge of thebattery is large. Since the prior art methods of determining theresidual capacity of batteries are applicable only to specificbatteries, respectively and hence each battery requires a specificcontrol.

The system proposed to eliminate memory effect (Japanese PatentLaid-open (Kokai)No. 4-308429) and the system proposed to preventovercharge (Japanese Patent Laid-open (Kokai) No. 61-81139) are intendedto suppress the deterioration of a battery and to simplify a chargingmethod when the battery is used as the power supply of portableapparatuses. Such a charge/discharge control method taking thecharacteristics and the history of batteries has not been proposed.

The difference between diurnal power demand and nocturnal power demandhas progressively increased in recent years, and diurnal power demand insummer is approaching the upper limit of total power generating abilityof power stations. Power storage techniques are effective means forsolving problems attributable to the wide daily and seasonal variationof power demand. For example, electric power storage methods publishedin Denki Gakkai-shi, Vol. 111, No. 3, pp. 185-188 (1992) and suchinstall large-capacity secondary batteries in a substation to store (tocharge) surplus electric power generated in the nighttime and to deliver(discharge) the stored power when power demand reaches a peak in thedaytime. However, nothing is mentioned about concrete means for themaintenance of soundness of the secondary batteries and the effectiveuse of residual power.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide adistributed electric power storage system capable of maintaining thesoundness of secondary batteries and of effectively using residualpower.

The present invention provides a secondary battery electric powerstorage system comprising a secondary battery connected to a load, and aconnector unit capable of being connected to a power system andconnected to the secondary battery and a plurality of loads,characterized by a controller for controlling the connection unitaccording to information about the secondary battery and the pluralityof loads.

At least either the plurality of loads or the secondary battery isconnected to the controller by an information transmitting means. Asecondary battery electric power storage system comprising:

-   -   a secondary battery connected to a load;    -   a detecting device for detecting a residual electric power of        said secondary battery;    -   a connection unit connected to a power source and to said        secondary battery;    -   a control unit connected to said charge/discharge unit; and    -   a signal line for transmitting information on said load and said        secondary battery to said control unit, wherein said connection        unit discharges electric power of said secondary battery to said        load when said residual electric power is larger than a        predetermined value and when the residual electric power is        smaller than the predetermined value, the electric power is        discharged to said power system or said load through said        connection unit, prior to charging of said secondary battery. A        secondary battery electric power storage system , wherein said        secondary battery is connected to a plurality of loads, and        wiring is provided for signaling and for transmitting        information on said loads and said secondary battery to said        control unit, wherein said connection unit distributes electric        power of said secondary battery among said loads when said        residual electric power is larger than the predetermined value.        A secondary battery electric power storage system comprising: a        secondary battery connectable to a load; a connection unit        connectable to the secondary battery, said connection unit being        connectable to a power system and either a plurality of loads or        a plurality of electric power strage units; a detecting device        for detecting a residual electric power in the secondary        battery; and a control unit for controlling the connection unit        on the basis of information from the secondary battery and at        least one of the loads or electric power strage units, wherein        electric power in the secondary battery is discharged to at        least one of the loads when the residual electric power is        larger than the predetermined value, and the residual electric        power is discharged to the power system or to at least one of        the loads or electric power strage units when the residual        electric power is smaller than the predetermined value, prior to        charging of the secondary battery. A secondary battery electric        power storage system comprising: a secondary battery connected        to a load; a connection unit connectable to the secondary        battery, said connection unit being connectable to a power        system and either a plurality of loads or a plurality of        electric power strage units; a detecting device for detecting a        residual electric power in the secondary battery; and a control        unit for controlling the connection unit on the basis of        information from the secondary battery and at least one of the        loads or electric power strage units, wherein electric power in        the secondary battery is discharged to at least one of the loads        when the residual electric power is larger than the        predetermined value, and the residual electric power is        discharged to the power system or to at least one of the loads        or electric power strage units when the residual electric power        is smaller than the predetermined value, prior to charging of        the secondary battery. A secondary battery electric power        storage system, wherein said connection unit is connected to        either a plurality of loads or a electric power strage units,        and said signal line for transmitting information on either said        loads or said electric power strage units and said secondary        battery to said control unit, wherein said connection unit        distributes electric power of said secondary battery among said        either said loads or said electric power strage units when said        residual electric power is larger than the predetermined value.

The secondary battery electric power storage system is characterized bya signal line to transmit the information about the operating conditionof the plurality of loads to the controller, and a signal line fortransmitting information about the surplus electric power of thesecondary battery to the controller.

The secondary battery electric power storage system may be provided withat least either a measuring means assocaited with the plurality of loadsto measure information about operating condition or a measuring meansassociated with the secondary battery to measure information about thesurplus electric power. The measuring means may be ordinary measuringmeans (sensors) suitable for the purpose of measurement.

The secondary battery electric power storage system is characterizedalso by the connection of a plurality of electric power storage units tothe connection unit, and the connection of the plurality of electricpower storage units and the controller by an information transmittingmeans.

The plurality of electric power storage units may be provided with ameasuring means for measuring the condition of power storage. Themeasuring means may be an ordinary measuring means (sensor) suitable forthe purpose of measurement.

The present invention is applicable to, for example, the secondarybatteries of electric vehicles, the second batteries of hotwater supplysystems, secondary batteries for illumination, secondary batteries forair-conditioning systems, buildings, factories, apartment houses, citiesand general residential buildings provided with power supply facilities,such as emergency power supplies, and transport facilities usingelectric power.

Desirably, the controller is provided with a clock or a timer.

The present invention provides also a secondary battery electric powerstorage system comprising a secondary battery connected to loads, and aconnection unit capable of being connected to a power system, andconnected to the secondary battery and at least either a plurality ofloads or a plurality of electric power storage units, characterized inthat a load to which power is to be fed and the capacity are selected onthe basis of information about the secondary battery, the plurality ofloads and the plurality of electric power storage units, and the surpluselectric power remaining in the secondary battery after feeding thepower stored in the secondary battery to the loads is fed to theselected load.

A load to which electric power is to be fed and the capacity areselected on the basis of at least one of information about the surpluselectric power of the secondary battery, information about the operatingcondition of the plurality of loads and information about the powerstorage condition of the electric power storage units, and power is fedto the selected load.

The electric power storage system of the present invention may employthe following secondary battery electric power storage system forcontrolling the power system or operations for charging and dischargingelectric power stored in a secondary battery and a plurality of electricpower storage units.

The present invention provides a electric power storage systemcomprising a connection unit connectable to a power system, andconnected to at least either a plurality of loads or a plurality ofelectric power storage units, a controller for controlling theconnection unit, and a connecting means for connecting a secondarybattery, characterized in that the controller controls the connectionunit on the basis of information from at least one of the plurality ofloads, the plurality of electric power storage units and the connectingmeans.

The secondary battery electric power storage system is characterizedalso by an information transmitting means interposed between at leastone of the plurality of loads, the plurality of electric power storageunits and the connecting means, and the controller. A secondary batteryis connected for charging and discharging to the secondary battery powerstorage system to use power effectively.

At least one of the plurality of loads, the plurality of electric powerstorage units and the connecting means is provided with measuring meansfor measuring various values, assocaited with the informationtransmitting means. The information transmitting means transmitsinformation measured by the measuring means.

The secondary battery to be employed in the present invention isprovided with a measuring means for measuring the amount of electricpower charged in the secondary battery and the amount of electric powerdischarged from the secondary battery, and a computer that calculatesthe residual power of the secondary battery.

More concretely, the secondary battery electric power storage system isprovided with a measuring means for measuring the condition of thesecondary battery, and a computer provided with a memory capable ofstoring measured data measured by the measuring means, arithmeticprograms and information including data on the characterisitics of thesecondary battery, and a controller for processing the informationstored in the memory and information given thereto from externaldevices, and it is desirable that the information stored in thesecondary battery can be transmitted by the information transmittingmeans.

The secondary battery to be used by the present invention is at leastone of secondary batteries including lead-acid batteries, nickel-cadmiumbatteries, nickelhydrogen batteries and lithium batteries, or anycombination of these secondary batteries. The secondary battery isprovided with a storage device capable of storing at least the measureddata and the arithmetic programs.

The plurality of electric power storage units are at least a pluralityof secondary batteries, such as lead-acid batteries, nickel-cadmiumbatteries, nickel-metal hydride batteries or lithium batteries, aplurality of heat storage and heat exchanger systems, a plurality ofsuperconducting type electric power storage systems, or any combinationsof these batteries and electric power storage systems.

The connection unit is provided with an ac-dc conversion means and aswitching means. The ac-dc conversion means, such as a thyristor,enables the control of power factor. The switching means switchescircuits connecting the power system to the secondary battery, theplurality of loads and the plurality of electric power storage unitsdepending on the operating condition of the surrounding loads. Whennecessary, the secondary battery electric power storage system isprovided with a power measuring means for measuring the amount of powerfed or received through the connecting unit, such as a measuring meansfor measuring the amount of charged electric power and the amount ofdischarged electric power, and an information transmitting means fortransmitting the measured data to the controller for controlling theconnection unit. The secondary battery or the plurality of electricpower storage units may be provided with a measuring means for measuringthe amount of charged electric power and that of discharged electricpower.

The means for measuring the amount of charged electric power and that ofdischarged electric power is a sensor, such as an ammeter voltmeter or aCoulomb meter.

The controller for controlling the connection unit is capable ofselecting a load to which the secondary battery and the electric powerstorage units feed power on the basis of information about the amount ofthe surplus electric power of the secondary battery, operating conditionof the plurality of loads and the power storage condition of theplurality of electric power storage units. The secondary battery powerstorage system may be provided with a calculating means for calculatingthe amount of charged electric power and that of discharged electricpower on the basis of information from the secondary battery, theplurality of loads and the plurality of electric power storage units andwith a memorijing means.

The information about the operating condition of the plurality of loadsis information about power necessary for operating the plurality ofloads or the current power demand of the plurality of loads. Preferably,information about scheduled operating time and such is used.

The information transmitting means is, for example, a signal line.Information may be transmitted by means of radiowaves.

The information about the surplus electric power is, for example, ameasured amount of surplus electric power, data on optimum charge anddischarge characteristics (charge and discharge modes) and the chargeand discharge history of the secondary battery.

The plurality of loads has at least one load, and the plurality ofelectric power storage units has at least one electric power storageunit.

A secondary battery electric power storage system in accordance with thepresent invention comprises a secondary battery mounted on a load, suchas an electric vehicle, a connection unit capable of being connected toa power system, such as a charge stand, and connected to the secondarybattery, a plurality of electric power storage units capable of beingconnected to the power system, and connected through the connection unitin parallel to the secondary battery, a plurality of loads connected tothe plurality of electric power storage unit, a plurality of loadsconnected to the connection unit.

The connection unit capable of being connected to the power system maybe connected to the secondary battery, the plurality of loads and theplurality of electric power storage units.

The present invention is capable of controlling charge and discharge ofthe plurality of loads, the plurality of electric power storage unitsand the secondary battery on the basis of information from the pluralityof loads, the plurality of electric power storage units and thesecondary battery.

Concretely, necessary power can be measured by a power measuring meanson the basis of the operating condition of the plurality of loads. Thesurplus electric power of the secondary battery, the power storagecondition of the plurality of electric power storage units, and thedischarge characteristic and the available capacity of the battery aredetermined, a load to which power is to be fed is selected from amongthe plurality of loads or the plurality of electric power storage units,and the surplus electric power can be fed through the connection unit tothe selected load.

Naturally, power may be stored in the electric power storage units andthen power may be fed from the electric power storage units to theplurality of loads.

Thus the surplus electric power can be effectively distributed and theresidual power can be discharged after determining the amount ofavailable power from the residual power. Therefore, the soundness of thebattery can be secured and discharge control can be efficiently carriedout.

When charging the secondary batter, the residual capacity of thesecondary battery is determined before charging, and whether theseoncary battery is to be charged or whether the secondary battery isdischarged is determined on the basis the residual capacity of thesecondary battery.

The intrinsic optimum charge and discharge characteristics of thesecondary battery, and the power demand of the plurality of loads or thepower storage condition of the plurality of electric power storage unitsare measured and a load to which power is to be fed is selected. Whenthe plurality of loads has a plurality of loads, it is preferable tomeasure the power demand of each load. When the plurality of electricpower storage units has a plurality of electric power storage units, itis preferable to determine the power storage condition of each electricpower storage unit.

For example, a load to which power is to be fed and the amount of powerto be fed are determined selectively after examining power demand to seeif the power demand can be supplied by the secondary battery and to seeif the output current density (large-current discharge or small-currentdischarge) is appropriate to the secondary battery, and then theconnection unit connects the secondary battery to the selected load tofeed power to the latter by orders of controller.

When the timer is used, the soundness of the battery can be secured andelectric power can be efficiently used by accumulating electric power innight period rate hours in the night and using the accumulated electricpower in the daytime.

More concretely, for example, the secondary battery is charged throughthe connection unit with electric power during night period rate hours,the surplus electric power of the secondary battery is fed (discharged)to the connection unit connected to the secondary battery, and electricpower is fed (discharged) through the connection unit to the pluralityof electric power storage units, the plurality of loads connected to theplurality of electric power storage units and the plurality of loadsconnected to the connection unit in day period rate hours. Inexpensivenight period rate electric power can be stored and used, and then thestored electric power can be sold through the connection unit that canbe connected to the secondary battery to consumers in day. When sellingthe stored electric power, it is preferable to determine the powerdemand of the plurality of loads on the basis of information aboutoperating condition received from a plurality of electric power storageunits or the plurality of loads by the controller connected to theconnection unit connected to the secondary batteries, to select a loadto which electric power is to be fed, taking into consideration theavailable power capacity of the secondary battery, and to feed thesurplus electric power of the secondary battery through the connectionunit to the selected load.

The soundness and the original power capacity of the battery can beknown by discharging the surplus electric power. The original powercapacity of the battery can be known from charged capacity afterdischarge of nearly 100% of the full capacity of the battery (nearlyexhausted state). it is desirable, if possible, to know the capacity ofthe battery every time the battery is discharged or charged to know thesoundness of the battery.

Desirably, the secondary battery employed in the present invention isprovided with, for example, measuring means (sensors) for acquiringdata, an A/D converter for converting the data acquired by the measuringmeans and giving the converted data to a computer, a memory storing dataon the charge and discharge history, arithmetic programs, an indicationprogram and data on the standard characteristics, and a controller forprocessing the information stored in the memory and information placedinto the memory by external devices. These components may be integrallycombined with the battery.

For example, the arithmetic programs and the indication program are anarithmetic program defining a procedure for determining dischargedcapacity by integrating discharge current, an arithmetic programdefining a procedure for determining charged capacity by integratingcharge current, an arithmetic program defining a procedure fordetermining converted charged capacity, i.e., available capacity under adischarge rate and a temperature condition at the time when dischargecurrent data is received from the discharge efficiency and thetemperature characteristic, determined by converting charged capacity ina real-time mode, an arithmetic program defining a procedure fordetermining surplus electric power discharged capacity by integratingsurplus electric power discharge current data, and an indication programdefining a procedure for indicating the surplus electric powerdischarged capacity determined by the procedure defined by thearithmetic program.

Discharge current data, discharge voltage data and discharge temperaturedata on the discharge history, are measured by measuring means (sensors)when the secondary battery feeds electric power to the loads, and themeasured data are transferred through an A/D converted to a computerprovided with a memory and a controller. Charging current data, chargevoltage data and charge temperature data on the charge history, aremeasured when the secondary battery is charged with electric powerthrough the connection unit connected to the secondary battery in thenight, and the measured data are transferred through the A/D converterto the computer. Surplus electric power discharge current data, surpluselectric power discharge voltage data and surplus electric powerdischarge temperature on surplus electric power discharge history, aremeasured by sensors when the secondary battery discharges surpluselectric power through the connection unit connected to the secondarybattery, and the measured data are transferred through the A/D converterto the computer. The soundness of the battery can be known from thosemeasured data. A discharged capacity discharged to the loads and asurplus electric power discharged capacity discharged to the connectionunit can be known from the discharge current data and the surpluselectric power discharge current, and the discharge operation of thesecondary battery can be controlled so that the battery may not bedischarged to a voltage below the final discharge voltage, i.e., so thatthe secondary battery may not be overdischarged, by using the dischargevoltage data and the surplus electric power discharge voltage data. Thecharged capacity charged into the secondary battery can be known fromthe charge current data. The increase of the voltage of a lithiumbattery to its final charge voltage can be known from the charge voltagedata and hence the overcharge of the lithium battery can be prevented.The final charge voltage of a nickel-cadmium battery can be known fromthe variation of the voltage in the final stage of charging operationand hence charging can be terminated before the nickel cadmium batteryis overcharged.

Unlike a nickel-cadmium battery, a nickel-metal hydride battery has asmall voltage variation in the final stage of charging. Therefore, it isdesirable to take temperature variation into consideration in additionto voltage variation in determining the time to stop charging to preventovercharge. As regards other kinds of batteries, abnormal rise oftemperature is an indication of the abnormal condition of the batteries.Since charging efficiency and discharging efficiency are dependent ontemperature, it is preferable to use temperature data in correctingcharged capacity and discharged capacity because charged capacity anddischarged capacity are dependent on temperature.

Desirably, the aforesaid data are corrected for charging rate,discharging rate and temperature. The standard characteristic data, suchas a the inherent charging efficiency, discharging efficiency andtemperature characteristic, of the secondary battery are stored in thememory. The charge current data and the discharge current data given tothe A/D converter are integrated to determine charged capacity anddischarged capacity. The charged capacity is converted in a real-timemode into a converted charged capacity, i.e., a capacity available atthe discharge rate and under the temperature condition at the time whenthe discharge current data is obtained, on the basis of the chargingefficiency, the discharging efficiency and the temperaturecharacteristic stored in the memory. The discharged capacity issubtracted from the converted charged capacity determined in thereal-time mode to determine a residual capacity. Thus, the residualcapacity at the current temperature and at the current discharge ratecan be indicted. For example, since the possible distance of travel ofan electric vehicle is dependent on the condition of the road, namely,the possible distance of travel along a downhill is longer than thatalong an uphill, the possible distance of travel can be estimated on thebasis of the discharging efficiency according to the condition of theroad, and the estimated possible distance of travel can be indicated.

Since the discharging efficiency is dependent on temperature and issubject to seasonal variation, a possible distance of travel determinedby taking into consideration the temperature characteristic can beindicated.

Surplus electric power discharge capacity can be determined byintegrating the surplus electric power discharge current data and thesurplus electric power discharge capacity can be indicated. Since thesurplus electric power discharge capacity is selling electric energy forsale, the surplus electric power discharge capacity is transferred tothe connection unit connected to the secondary battery and the powersystem, the plurality of electric power storage units or the pluralityof loads. Preferably the connection unit is capable of measuring andindicating the capacity.

It is desirable to discharge the surplus electric power from thesecondary battery in a mode conforming to optimum discharge conditionsfor the secondary battery to secure the soundness of the secondarybattery and to extend the cycle like of the secondary battery. It ispreferable to discharge the surplus electric power from the secondarybattery in conformance with optimum discharge conditions stored in thememory when the surplus electric power is discharged to the connectionunit connected to the secondary battery and connectable to the powersystem. The optimum charge and discharge conditions are pieces ofinformation about a discharge method specifying, for example, at leastone of maximum discharge capacity, discharge current, discharge voltage,discharge time and a lower limit voltage. More concretely, dischargingconditions as battery characteristic data including discharge modes,such as a constant-current discharge mode, a constant-voltage dischargemode, a pulse discharge mode and combinations of those discharge modes,an optimum current, an optimum voltage, and discharge cutting mode, suchas a time-cut mote and a voltage-cut mode, is stored beforehand in thememory. Charging information specifying charging conditions similar tothe discharging conditions are used for charging. If even one of thebatteries of a battery set is deteriorated, the deteriorated batterywill be overdischarged and the cycle life of the same is shortedsignificantly. It is desirable to use a control method determined bytaking into consideration the type the scale and the security of thebattery to execute time-cut or voltage-cut on the basis of monitoredvoltage variation.

The available discharge capacity that can be discharged in the future(next) discharge cycle and the cycle life of the secondary battery canbe estimated from the past charge capacities of the secondary batteryand the mode of change of charged capacity. Causes of reduction of thecapacity of the secondary battery, such as the exhaustion of theelectrolyte, the deterioration of the positive electrode and thedeterioration of the negative electrode, can be determined from the modeof reduction of the capacity. Overdischarge of the battery can beprevented by determining the available discharge capacity and thepossible discharge time of the battery and discharging the surplus poweraccordingly. Similarly, the secondary battery is charged in a modeconforming to the optimum charge conditions stored in the memory whencharging the secondary battery through the connection unit at night, inwhich overcharge of the secondary battery can be prevented bydetermining the available discharge capacity and the possible dischargetime, and charging the secondary battery accordingly.

It is desirable to determine beforehand surplus electric power dischargehours. For example, the discharge of the surplus electric power isinterrupted when the surplus electric power is not dischargedcompletely. The charge capacity determined in the preceding charge cycleis used as charge capacity. Preferably, the surplus electric powerdischarge capacity is determined on the basis of the residual capacity,taking into consideration the type of the battery to secure thesoundness of the battery. For example, since a nickel-cadmium batteryand a nickel-metal hydride battery are subject to large self-dischargeand have a memory effect, it is preferable to discharge 95% to 100% of adischarge capacity in a mode conforming to optimum discharge conditionsrevised for the future available discharge capacity of the batterieswhen the residual capacity is in the range of 0% to 85% of the chargecapacity. When the residual capacity is 85% or above of the chargecapacity, it is better not to discharge the surplus electric power.Thus, charging and discharging are simplified and the memory effect canbe prevented. Since a lithium battery or the like is subject to acomparatively small self-discharge and the cycle cycle life of a lithiumbattery or the like is reduced when the same is discharged deep, it isdesirable to discharge the surplus electric power corresponding to 80%to 95% of the discharge capacity in a mode conforming to optimumdischarge conditions revised for the available discharge capacity of thebattery, when the residual capacity is in the range of 5% to 80% of thecharge capacity. When the residual capacity is less than 5% of thecharge capacity, it is better not to discharge the surplus electricpower because further discharge reduces the cycle lief of the battery.When the residual capacity is 80% or above of the charge capacity, it isdesirable not to discharge the surplus electric power to simplifycharging and discharging.

The whole capacity of battery can be known at every discharge and theresidual capacity of the battery can be accurately determined when thesurplus electric power is discharged with the performance of the batterybeing taking into consideration. The cycle life of the battery and thefuture capacity of the battery can be estimated from the whole capacityof the battery and the residual capacity. Accordingly, connection unitcontrol can be carried out according to the change of the performance ofthe battery and thereby the soundless of the battery is enhanced.

Charging of the battery with the inexpensive night period rate electricpower in the nighttine and using the surplus electric power in thedaytime are economically advantageous.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a secondary battery electoric power storagesystem in accordance with the present invention;

FIG. 2 is a block diagram of a secondary battery electoreic powerstorage system in accordance with the present invention;

FIG. 3 is a block diagram of a secondary battery electoric power storagesystem in accordance with the present invention;

FIG. 4 is a block diagram of a secondary battery electoric power storagesystem in accordance with the present invention;

FIG. 5 is a flow chart of a procedure for controlling a secondarybattery, in accordance with the present invention;

FIG. 6 is a graph showing the connection unit cycle characteristics ofsecondary batteries in a second embodiment according to the presentinvention;

FIG. 7 is a graph comparatively showing residual capacity indicationsand actual residual capacities in the second embodiment according to thepresent invention;

FIG. 8 is a graph showing the connection unit cycles of secondarybatteries in a third embodiment according to the present invention;

FIG. 9 is a graph comparatively showing residual capacity indicationsand residual capacities in a comparative example 1; and

FIG. 10 is a graph showing the connection unit cycle characteristics ofsecondary batteries in the comparative example 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described indetail hereinafter.

The embodiments are illustrative and not restrictive.

First Embodiment

FIG. 1 shows a secondary battery electric power storage system in afirst embodiment according to the present invention. Although the firstembodiment is one of the best modes for carrying out the invention, thepresent invention is not limited thereto. Referring to FIG. 1, asecondary battery load 1 and a connection unit 2 connectable to a powersystem are connected to a secondary battery 3. A plurality of electricpower storage units 4 are placed in parallel combination with theconnection unit 2 connected to a power supply system. A plurality ofloads 5 are connected to the connection unit 2 or the electric powerstorage units 4. A signal line 30 indicated by broken lines is connectedto a controller 7 included in the connection unit 2. Ditecting device 40detect a residual electric power in the secondary battery.

When necessary, the secondary battery electric power storage system isprovided with a means, not shown in FIGS. 1 to 4, for supplying electricpower directly from the power supply system to the loads 5 or theelectric power storage units 4, bypassing the connection unit 2. Whenthe secondary battery electric power storage system is provided withsuch a means, it is desirable that the secondary battery electric powerstorage system is provided with a signal line for transmitting signalsrepresenting measured values, such as the amount of electric power usedto the controller 7 of the connection unit 2. Amounts of electric powerapplied to and delivered from the secondary battery 3 and the electricpower storage units 4 are measured by measuring devices and measureddata is sent through the signal line to the controller 7 of theconnection unit 2.

The secondary battery 3, the electric power storage units 4 and theloads 5 are provided with sensors (measuring means).

First the secondary battery 3 is connected to the connection unit 2 tocharge the secondary battery 3 with night period rate electric power.After the secondary battery has been charged, the secondary battery 3 isconnected to the secondary battery load 1 to discharge the secondarybattery 3. After discharging, the secondary battery 3 is disconnectedfrom the secondary battery load 1 and connected to the connection unit 2to discharge the surplus electric power of the secondary battery 3 inthe day period rate hours. A controller 6 included in the secondarybattery 3 controls the secondary battery 3 for discharging the surpluselectric power remaining after charging the secondary battery load 1,i.e., the residual capacity in a mode conforming to optimum dischargingconditions in the day period rate hours. The discharge of the surpluselectric power is stopped in the night period rate hours and thesecondary battery is charged. In this state, the charge capacity doesnot correspond to the capacity of the battery because the battery hasthe residual capacity. Therefore, the charge capacity used in thepreceding charge cycle is used as the charge capacity to be taking intoconsideration in indicating the residual capacity. The controller 7 ofthe connection unit 2 measures the amounts of electric power required bythe electric power storage units 4 or the loads 5, selects the electricpower storage unit or the load and controls the secondary battery 3 tosupply the surplus electric power to the selected electric power storageunit or the load.

FIG. 2 shows an embodiment of the present invention. In this embodiment,a secondary battery load 1 and a connection unit 2 connectable to apower system are connected to a secondary battery 3, and electric powerstorage units 4 are placed in parallel combination with the connectionunit 2.

FIG. 3 shows an embodiment of the present invention. In this embodiment,a secondary battery load 1 and a connection unit 2 connectable to apower system are connected to a secondary battery 3, and loads 5 areconnected to the connection unit 2. FIG. 4 shows an embodiment of thepresent invention. In this embodiment, a secondary battery load 1 and aconnection unit 2 connectable to a power system are connected to asecondary batter 3, and series circuits each of a electric power storageunit 4 and a load 5 are placed in parallel connection with theconnection unit 2.

Second Embodiment

FIG. 5 is a flow chart of a control procedure to be carried out by thecontrollers 6 of the secondary batteries 3 of FIGS. 1 to 4. The controlprocedure will be described hereinafter with reference to FIGS. 1 to 5.The secondary battery 3 is provided with the controller 6, an A/dconverter 8 and a memory 9. The memory 9 is capable of storing standardcharacteristic data on the intrinsic characteristics of the secondarybattery 3 including charging efficiencys 10, discharging efficiencys 11,temperature characteristics 12 and optimum charge and dischargeconditions 13. The optimum charge and discharge conditions 13 specifycharge and discharge modes, such as a constant-current charge mode,constant discharge mode, a constant-voltage discharge mode and aconstant -voltage discharge mode, currents and voltages, cut voltages,charge capacities, discharge capacities, charge times and dischargetimes.

When the secondary battery 3 is connected to the connection unit 2 forcharging, the secondary battery 3 is controlled for charging accordingto the optimum charge conditions. At every charge cycle, an A/Dconverter receives charge operation data including charge current data14, charge voltage data 15 and charge temperature data 16. The chargevoltage data 15 is necessary for terminating charging at a cut voltage.The charge temperature data 16 is used for detecting the final chargestage for a nickel-metal hydride battery. The temperature data 15 isused also for detecting the abnormal condition of the battery when thetemperature of the battery rises abnormally. The charge current data 14is integrated to obtain a charged capacity.

When the secondary battery 3 is connected to the secondary battery load1 and electric power stored in the secondary battery 3 is dischargedinto the secondary battery load 1, the A/D converter 8 receivesdischarge operation data including discharge current data 17, dischargevoltage data 18 and discharge temperature data 19. The discharge voltagedata 18 is necessary for terminating discharge at a cut voltage. Thedischarge current data 17 is integrated to obtain a discharged capacity.The discharged capacity is converted in a real-time mode for adischarging rate and a temperature represented by the dischargetemperature data 19 into an available discharge capacity, i.e.,converted charge capacity, for determining a residual capacity. Theresidual capacity is obtained by subtracting the discharged capacityfrom the converted charge capacity.

When the secondary battery 3 is connected to the connection unit 2 todischarge the surplus electric power, the discharge operation of thesecondary battery 3 is controlled according to the optimum charge anddischarge conditions 13. At every surplus electric power dischargingoperation, the A/D converter 8 receives surplus electric power dischargeoperation data including surplus electric power discharge current data20, surplus electric power discharge voltage data 21 and surpluselectric power temperature data 22. The surplus electric power dischargecurrent data 20 is integrated to obtain a surplus electric powerdischarge capacity, and the surplus electric power discharge capacity isindicated. The surplus electric power discharge capacity can betransferred through the connection unit 2 to the electric power storageunits 4 and the loads 5. When selling the surplus electric power, it ispreferable to indicate an amount of money corresponding to the surpluselectric power when necessary.

FIG. 6 shows the charge and discharge cycle characteristics of secondarybatteries and FIG. 7 shows the variation of the difference betweenresidual capacity indication and actual residual capacity with thenumber of charge and discharge cycles. The capacities of a lead-acidbattery B, a nickel-cadmium battery D, a nickel-hydrogen battery A andlithium battery E decrease slightly as the number of charge anddischarge cycles increases, and the possible numbers of charge anddischarge cycles for those batteries are not less than 1000. Thedifference between the residual capacity indication and the actualresidual capacity is very small.

Third Embodiment

When a secondary battery 3 is a nickel-cadmium battery or a nickel-metalhydride battery, a controller 6 controls the secondary battery 3 fordischarging so that 95% to 100% of a discharge capacity corresponding toan available discharge capacity is discharged in a mode conforming tooptimum discharge conditions when the residual capacity is 0 to 85% ofthe charge capacity of the secondary battery 3.

If the residual capacity is 85% or above of the charge capacity, surpluselectric power discharge is not performed. When the secondary battery 3is a lithium battery, the controller 6 controls the secondary battery 3so that 80% to 95% of a discharge capacity corresponding to an availabledischarge capacity is discharged in a mode conforming to optimumdischarge conditions when the residual capacity is 5% to 80% of thecharge capacity. When the residual capacity is 5% or below of the chargecapacity, surplus electric power discharge is not performed. When theresidual capacity is 80% or above of the charge capacity, surpluselectric power discharge is not performed.

FIG. 8 shows the charge and discharge cycle characteristics of batteriesunder the control operation of the controller. The capacities of anickel-cadmium battery, a nickel-metal hydride battery and a lithiumbattery decrease scarcely as the number of charge and discharge cyclesfor those batteries are not less than 1200.

COMPARATIVE EXAMPLE 1

In a secondary battery electric power storage system in a comparativeexample 1, a secondary battery load 1 and a connection unit 2 areconnected to a secondary battery 3. The secondary battery 3 is connectedto the connection unit 2 and the secondary battery 3 is charged withnight period rate electric power. Then, the secondary battery 3 isconnected to the secondary battery load 1 and the electric power storedin the secondary battery 3 is discharged into the secondary battery load1. After discharging, the secondary battery 3 is disconnected from thesecondary battery load 1 and is connected to the connection unit 2 tocharge the secondary battery 3 with night period rate electric power.The residual capacity of the secondary batter is determined bysubtracting a discharged capacity from an initial capacity. FIG. 9 showsthe difference between residual capacity indication and actual residualcapacity. As is obvious from FIG. 9, the difference increases as thenumber of charge and discharge cycles increases and, consequently,accurate residual capacity indication is impossible. FIG. 10 shows thecharge and discharge cycle characteristics of batteries. As is obviousfrom FIG. 10, the capacities of a lead-acid battery, a nickel-cadmiumbattery, a nickel-metal hydride battery and a lithium battery decreasegreatly as the number of charge and discharge cycles increases, and thelives of those batteries are in the range of 500 to 700 charge anddischarge cycles.

As is apparent from the foregoing description, according to the presentinvention, the soundness of the battery can be secured, and charging anddischarging are carried out efficiently. The secondary battery can becharged with inexpensive night period rate electric power in the nightand the surplus electric power can be supplied to loads in the day time.

1. An electric vehicle comprising: a secondary battery (3); a secondarybattery load (1) being connectable to said secondary battery (3); andmeans (7) for determining an available discharge capacity of saidsecondary battery (3) such that electric power in the secondary battery(3) is discharged when a determined surplus residual electric power ofsaid secondary battery (3) is within a predetermined range, prior tocharging of said secondary battery (3).
 2. An electric vehiclecomprising: a connection unit (2) connectable to at least one load (5);means for connecting said connection unit (2) to a secondary battery(3), said secondary battery (3) being connectable to a secondary batteryload (1); means (7) for determining an available discharge capacity ofsaid secondary battery (3); and control means (6) for controlling saidconnection unit (2) on the basis of information received from the atleast one load (5), such that electric power in the secondary battery(3) is discharged to a selected at least one of said at least one load(5) when a determined surplus residual electric power of said secondarybattery (3) is within a predetermined range, prior to charging of saidsecondary battery (3).
 3. An electric vehicle as claimed in claim 2,wherein said connection unit (2) is connectable to the at least one load(5) and to at least one electric power storage unit (4), wherein saidcontrol means (6) is for controlling said connection unit (2) on thebasis of information received from the at least one load (5) and the atleast one electric power storage unit (4).
 4. An electric vehiclecomprising: a connection unit (2) connectable to at least one electricpower storage unit (4); means for connecting said connection unit (2) toa secondary battery (3), said secondary battery (3) being connectable toa secondary battery load (1); means (7) for determining an availabledischarge capacity of said secondary battery (3); and control means (6)for controlling said connection unit (2) on the basis of informationreceived from the at least one electric power storage unit (4), suchthat electric power in the secondary battery (3) is discharged to aselected at least one of said at least one electric power storage unit(4) when a determined surplus residual electric power of said secondarybattery is within a predetermined range, prior to charging of saidsecondary battery (3).
 5. A vehicle comprising: a secondary battery; asecondary battery load being connectable to said secondary battery; andmeans for determining an available discharge capacity of said secondarybattery such that electric power in the secondary battery is dischargedwhen a determined surplus residual electric power of said secondarybattery is within a predetermined range, prior to charging of saidsecondary battery.
 6. A vehicle as claimed in claim 5, wherein thevehicle is an automobile.
 7. A vehicle comprising: a connection unitconnectable to at least one load means for connecting said connectionunit to a secondary battery, said secondary battery being connectable toa secondary battery load; means for determining an available dischargecapacity of said secondary battery; and control means for controllingsaid connection unit on the basis of information received from the atleast one load, such that electric power in the secondary battery isdischarged to a selected at least one of said at least one load when adetermined surplus residual electric power of said secondary battery iswithin a predetermined range, prior to charging of said secondarybattery.
 8. A vehicle as claimed in claim 7, wherein the vehicle is anautomobile.
 9. A vehicle as claimed in claim 7, wherein said connectionunit is connectable to the at least one load and to at least oneelectric power storage unit, wherein said control means is forcontrolling said connection unit on the basis of information receivedfrom the at least one load and the at least one electric power storageunit.
 10. A vehicle as claimed in claim 9, wherein the vehicle is anautomobile.
 11. A vehicle comprising: a connection unit connectable toat least one electric power storage unit; means for connecting saidconnection unit to a secondary battery, said secondary battery beingconnectable to a secondary battery load; means for determining anavailable discharge capacity of said secondary battery; and controlmeans for controlling said connection unit on the basis of informationreceived from the at least one electric power storage unit, such thatelectric power in the secondary battery is discharged to a selected atleast one of said at least one electric power storage unit when adetermined surplus residual electric power of said secondary battery iswithin a predetermined range, prior to charging of said secondarybattery.
 12. A vehicle as claimed in claim 11, wherein the vehicle is anautomobile.